Spatial Variability in Sedimentary Algal Microfossils and Its Bearing on Diatom-Inferred pH Reconstructions

1986 ◽  
Vol 43 (10) ◽  
pp. 1836-1845 ◽  
Author(s):  
Sushil S. Dixit ◽  
R. Douglas Evans
Keyword(s):  
Spatial Variability ◽  
Shallow Waters ◽  
Diatom Assemblages ◽  
Ph Indicator ◽  
Ph Profile ◽  
Sediment Samples ◽  
The Past ◽  
Acidic Nature ◽  
Inferred Ph ◽  
Water Depths

Spatial variability of algal microfossils was investigated in 20–21 surface (0–0.25 cm) sediment samples from Hannah and Clearwater lakes, Ontario, together with the variability in 20 downcore diatom-inferred pH profiles from Hannah Lake. Strong habitat-dependent spatial variability in the distribution of microfossils was observed in lakes of simple morphology. The abundance of planktonic taxa was high in deepwater sediments in both the lakes, while benthic taxa were common only in the sediments of shallow waters of Clearwater Lake. It is hypothesized that greater circulation and presence of sufficient light at all depths allowed benthic diatoms to flourish even in samples from the deep areas of Hannah Lake. The use of pH indicator diatom assemblages rather than individual taxa greatly reduced the variability in computing diatom-inferred pH. The variations were negligible within the samples collected from greater water depths. Results suggest that a single paleo-pH profile will provide an indication of the direction in change in pH, but that absolute pH results can be obtained only by utilizing several cores from many depth strata. The ability of index α and index B to accurately predict recent pH shifts of Hannah Lake was impaired because of its very acidic nature (pH < 4.5) in the past.

Assessment of Changes in Lake Water Chemistry in Sudbury Area Lakes since Preindustrial Times

1992 ◽  
Vol 49 (S1) ◽  
pp. 8-16 ◽  
Author(s):  
Sushil S. Dixit ◽  
Aruna S. Dixit ◽  
John P. Smol
Keyword(s):  
Lake Water ◽  
Acidic Ph ◽  
Prevailing Wind ◽  
Alkaline Ph ◽  
Sediment Samples ◽  
Ion Concentrations ◽  
The Past ◽  
Lake Water Chemistry ◽  
Water Ph ◽  
Inferred Ph

Surface (recent) and bottom (pre-1880s) sediment samples from each of 72 Sudbury area lakes were analyzed for diatom valves and chrysophyte scales, and using these microfossils, we inferred changes in lake water pH, [Al], [Ni], conductance, and [Ca]. The study shows that extensive acidification has occurred in presently acidic (pH < 6.0) Sudbury lakes. Inferred [Al] has also increased in these lakes. The region also contains a few naturally acidic lakes; however, even these lakes have acidified further since the bottom sediments were deposited. Lakes that have current measured pH between 6.0 and 7.0 have either declined or increased in inferred pH in the past, whereas all lakes that are presently alkaline (pH > 7.0) have become more alkaline. The increase in inferred [Ni] in most of the study lakes indicates that Ni inputs are mainly atmospheric. Our data suggest that, in general, ion concentrations have increased in Sudbury lakes. The extent of acidification or alkalification in Sudbury lakes was primarily a function of proximity of the lakes to the smelters, orientation of prevailing wind patterns, and differences in watershed geology.

Holocene diatom assemblages from Dunderbukhta sediments, West Svalbard

2019 ◽  
pp. 242-245
Author(s):  
Ksenya V. Poleshchuk ◽  
Zinaida V. Pushina ◽  
Sergey R. Verkulich
Keyword(s):  
Environmental Changes ◽  
Ecological Groups ◽  
Diatom Assemblages ◽  
Diatom Analysis ◽  
Diatom Flora ◽  
Sediment Samples ◽  
Ecological Zones ◽  
Middle Holocene ◽  
Temperature Trends

The diatom analysis results of sediment samples from Dunderbukta area (Wedel Jarlsberg Land, West Svalbard) are presented in this paper. The diatom flora consists of four ecological groups, which ratio indicates three ecological zones. These zones show environmental changes of the area in early–middle Holocene that is demonstrating periods of regression and temperature trends.

scholarly journals A new diatom training set for the reconstruction of past water pH in the Tatra Mountain lakes

2021 ◽  
Author(s):  
Elwira Sienkiewicz ◽  
Michał Gąsiorowski ◽  
Ladislav Hamerlík ◽  
Peter Bitušík ◽  
Joanna Stańczak
Keyword(s):  
Surface Sediments ◽  
Tatra Mountains ◽  
Training Set ◽  
Statistical Parameters ◽  
The Past ◽  
Water Ph ◽  
Inferred Ph ◽  
The 1960S ◽  
The Tatra Mountains ◽  
The Relationship

AbstractLakes located in the Polish and Slovak parts of the Tatra Mountains were included in the Tatra diatom database (POL_SLOV training set). The relationship between the diatoms and the water chemistry in the surface sediments of 33 lakes was the basis for the statistical and numerical techniques for quantitative pH reconstruction. The reconstruction of the past water pH was performed using the alpine (AL:PE) and POL_SLOV training sets to compare the reliability of the databases for the Tatra lakes. The results showed that the POL_SLOV training set had better statistical parameters (R2 higher by 0.16, RMSE and max. bias lower by 0.2 and 0.36, respectively) compared to the AL:PE training set. The better performance of the POL_SLOV training set is particularly visible in the case of Przedni Staw Polski where the curve of the inferred water pH shows an opposite trend for the period from the 1960s to 1990 compared to that based on the AL:PE dataset. The reliability of the inferred pH was confirmed by the comparison with current instrumental measurements.

Levels of Spatial Variability: The “Community” Problem

1990 ◽  
Vol 5 ◽  
pp. 13-30 ◽  
Author(s):  
D. A. Springer ◽  
A. I. Miller
Keyword(s):  
Community Structure ◽  
Spatial Variability ◽  
Species Distribution ◽  
Distribution Patterns ◽  
The Past ◽  
Structure And Dynamics ◽  
Evolutionary Units ◽  
The Way

The way we view species distribution patterns, particularly at the level commonly referred to as the “community”, has changed over the past 70 years in biology and, subsequently, in paleontology. Because the degree to which species associations can be interpreted as ecological and evolutionary units depends ultimately on recognition and interpretation of faunal spatial variability, we need to understand the nature of this variability at all levels of resolution before we can adequately address questions of “community” structure and dynamics. While it is possible to recognize spatial variability at several levels, from the distributions of individuals within a species to the overall pattern created by the global biota, we must ask whether these patterns really comprise a hierarchy with natural discontinuities (Fig. 1), or whether it is more realistic to view them as a continuous variability spectrum.

scholarly journals EXTREME WAVE PRESSURES AND LOADS ON A PILE-SUPPORTED WHARF DECK - INFLUENCES OF AIR GAP AND WAVE DIRECTION

2018 ◽  
pp. 5
Author(s):  
Andrew Cornett
Keyword(s):  
Offshore Structures ◽  
Model Tests ◽  
Scale Model ◽  
Extreme Waves ◽  
Wave Direction ◽  
Coastal Structures ◽  
Extreme Wave ◽  
Wave Impact ◽  
The Past ◽  
Water Depths

Many deck-on-pile structures are located in shallow water depths at elevations low enough to be inundated by large waves during intense storms or tsunami. Many researchers have studied wave-in-deck loads over the past decade using a variety of theoretical, experimental, and numerical methods. Wave-in-deck loads on various pile supported coastal structures such as jetties, piers, wharves and bridges have been studied by Tirindelli et al. (2003), Cuomo et al. (2007, 2009), Murali et al. (2009), and Meng et al. (2010). All these authors analyzed data from scale model tests to investigate the pressures and loads on beam and deck elements subject to wave impact under various conditions. Wavein- deck loads on fixed offshore structures have been studied by Murray et al. (1997), Finnigan et al. (1997), Bea et al. (1999, 2001), Baarholm et al. (2004, 2009), and Raaij et al. (2007). These authors have studied both simplified and realistic deck structures using a mixture of theoretical analysis and model tests. Other researchers, including Kendon et al. (2010), Schellin et al. (2009), Lande et al. (2011) and Wemmenhove et al. (2011) have demonstrated that various CFD methods can be used to simulate the interaction of extreme waves with both simple and more realistic deck structures, and predict wave-in-deck pressures and loads.

scholarly journals Rapid climate change results in long-lasting spatial homogenization of phylogenetic diversity

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Bianca Saladin ◽  
Loïc Pellissier ◽  
Catherine H. Graham ◽  
Michael P. Nobis ◽  
Nicolas Salamin ◽  
...  
Keyword(s):  
Climate Change ◽  
Spatial Variability ◽  
Phylogenetic Diversity ◽  
Climate Changes ◽  
Northern Europe ◽  
Seed Plants ◽  
Climate Oscillations ◽  
The Past ◽  
Rapid Climate Change ◽  
Insight Into

Abstract Scientific understanding of biodiversity dynamics, resulting from past climate oscillations and projections of future changes in biodiversity, has advanced over the past decade. Little is known about how these responses, past or future, are spatially connected. Analyzing the spatial variability in biodiversity provides insight into how climate change affects the accumulation of diversity across space. Here, we evaluate the spatial variation of phylogenetic diversity of European seed plants among neighboring sites and assess the effects of past rapid climate changes during the Quaternary on these patterns. Our work shows a marked homogenization in phylogenetic diversity across Central and Northern Europe linked to high climate change velocity and large distances to refugia. Our results suggest that the future projected loss in evolutionary heritage may be even more dramatic, as homogenization in response to rapid climate change has occurred among sites across large landscapes, leaving a legacy that has lasted for millennia.

F(P)SO Global Responses in the West of Africa Squall Environment

2005 ◽  
Author(s):  
Zhibin Zhong ◽  
Yong Luo ◽  
Dusan Curic
Keyword(s):  
Time Series ◽  
Wind Speed ◽  
Wind Direction ◽  
Time History ◽  
The Past ◽  
Transient Nature ◽  
Time Histories ◽  
The Time Domain ◽  
Water Depths ◽  
Tandem Offloading

Mooring design for F(P)SOs in West of Africa offshore environment is in many cases governed by the squall driven condition. In the past, the squall condition was typically analyzed by using the peak wind speed with associated wind direction. However, due to its inherent transient nature, the squall event formulated in the time history with varying wind speed and direction is more appropriate and could be potentially more critical for the mooring system design. This approach has been adopted in the design and analysis of recent F(P)SO mooring systems. The F(P)SOs are turret-moored in various water depths in offshore West of Africa. A series of squall time histories have been applied to predict the global responses of the F(P)SO in the time domain. Each squall time history, which provides a unique combination of wind speed and direction variations, is analyzed in five nominal directions covering a sector of 90 degrees from East to West. Squall time histories are also applied to analyze the tandem offloading operation. The results are compared with those of the conventional constant wind speed approach and a few interesting observations are made. The paper also provides some insights into the F(P)SO yaw motions, as well as their relations to the changing wind direction. Analysis results demonstrate that using the squall time series with changing wind speed and direction is more critical than the conventional constant wind speed approach in the tandem offloading scenario. It is therefore recommended that mooring analysis using squall time series should at least be used for the tandem offloading simulations.

Sea Trial Results of ROV “ABISMO” for Deep Sea Inspection and Sampling

2008 ◽  
Author(s):  
Tomoya Inoue ◽  
Hiroyuki Osawa ◽  
Hiroshi Yoshida ◽  
Junichiro Tahara ◽  
Shojiro Ishibashi ◽  
...  
Keyword(s):  
Water Depth ◽  
Deep Sea ◽  
Earth Science ◽  
Sagami Bay ◽  
Sampling System ◽  
Sediment Samples ◽  
Sea Trial ◽  
The Third ◽  
Onboard Equipment ◽  
Water Depths

JAMSTEC (Japan Agency for Marine-Earth Science and Technology) has been developing the deep sea ROV ABISMO (Automatic Bottom Inspection and Sampling Mobile) having the capability to dive to the deepest sea. The purposes of ABISMO are to inspect on the seabed in the deep sea and to obtain sediment samples from there. ABISMO consists of a launcher and a vehicle which is launched from the launcher and surveys on the seabed to determine the place for sampling. Core sampling system, which is exchangeable with a gravity piston type or a grab type, is equipped in the launcher. The both of the launcher and the vehicle have cameras to observe. One of the features of ABISMO is that the vehicle has crawlers in addition to thrusters in order to advance mobility. ABISMO is operated with the support ship KAIREI and dived by means of its onboard equipment including a primary cable. We conducted sea trials in January and September 2007 at the areas with the water depths up to 1,300m in Sagami Bay as primary function tests. And we conducted the third sea trial at Izu-Ogasawara trench in December 2007 and made the successful results of diving to the depths up to 9707 m and obtaining a sediment sample from the seabed in 9760 m water depth. This paper describes the features and the outline of ABISMO as well as the sea trial results.

Holocene Relative Sea Level Changes along the Seattle Fault at Restoration Point, Washington

2000 ◽  
Vol 54 (3) ◽  
pp. 384-393 ◽  
Author(s):  
Brian L. Sherrod ◽  
Robert C. Bucknam ◽  
Estella B. Leopold
Keyword(s):  
Sea Level ◽  
Environmental Changes ◽  
Hanging Wall ◽  
Sea Level Changes ◽  
Diatom Assemblages ◽  
Recent Event ◽  
Plant Seed ◽  
The Past ◽  
The One ◽  
Fossil Diatoms

At a marsh on the hanging wall of the Seattle fault, fossil brackish water diatom and plant seed assemblages show that the marsh lay near sea level between ∼7500 and 1000 cal yr B.P. This marsh is uniquely situated for recording environmental changes associated with past earthquakes on the Seattle fault. Since 7500 cal yr B.P., changes in fossil diatoms and seeds record several rapid environmental changes. In the earliest of these, brackish conditions changed to freshwater ∼6900 cal yr B.P., possibly because of coseismic uplift or beach berm accretion. If coseismic uplift produced the freshening ∼6900 cal yr B.P., that uplift probably did not exceed 2 m. During another event about 1700 cal yr B.P., brackish plant and diatom assemblages changed rapidly to a tidal flat assemblage because of either tectonic subsidence or berm erosion. The site then remained a tideflat until the most recent event, when an abrupt shift from tideflat diatoms to freshwater taxa resulted from ∼7 m of uplift during an earthquake on the Seattle fault ∼1000 cal yr B.P. Regardless of the earlier events, no Seattle fault earthquake similar to the one ∼1000 cal yr B.P. occurred at any other time in the past 7500 years.

Within-year spatio-temporal variation in meiofaunal abundance and community structure, Sinop Bay, the Southern Black Sea

2016 ◽  
Vol 45 (1) ◽  
Author(s):  
Derya Ürkmez ◽  
Murat Sezgin ◽  
Melek Ersoy Karaçuha ◽  
İbrahim Öksüz ◽  
Tuncer Katağan ◽  
...  
Keyword(s):  
Community Structure ◽  
Temporal Variation ◽  
Surface Area ◽  
Black Sea ◽  
Sediment Samples ◽  
Core Sampler ◽  
Spatio Temporal ◽  
Meiofaunal Abundance ◽  
Water Depths

AbstractThe first comprehensive meiobenthos study was carried out in Turkey, the Southern Black Sea (Sinop) from August 2009 to July 2010.Sediment samples were collected monthly at eight stations at 3 m and 10 m water depths located on four transects. A metal push core sampler (surface area 12.56 cm

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